1. Field of the Invention
The present invention relates to an improvement on a light measuring device having an integration-type light measuring sensor.
2. Description of Related Art
Some of known exposure computing devices use multiple-divided integration-type light measuring sensors arranged to logarithmically compress an electrical signal from a light receiving part and to output the compressed signal as a light measurement output measured by each pixel. To have one and the same specific output value from all the pixels of the light measuring sensor for a field having uniform distribution of luminance which varies, the exposure computing device of this kind is arranged to make level correction and gain correction on each pixel of the light measuring sensor and to compute an exposure value on the basis of these correction values and the output values of the light measuring sensor. A memory which is provided for storing correction values is arranged to store the level correction value and gain correction value for each of pixels. Assuming that a storage capacity of 1 byte is necessary per pixel for storing each of the level correction value and gain correction value, in the case of a light measuring sensor which is divided into six parts, i.e., pixels, for example, a storage capacity necessary for correction of all pixels is "2 bytes.times.6=12 bytes".
To broaden the dynamic range of the integration-type light measuring sensor, the integration period of the light measuring sensor is sometimes varied according to changes taking place in luminance of a field. Therefore, in order to obtain a highly reliable exposure value, it has been necessary to correct the sensor outputs for a plurality of integration periods. Then, in the case of the above-stated light measuring sensor divided into six parts, if this sensor is arranged to be capable of coping with five different integration periods, the memory which stores sensor-output correction values must be arranged to have a storage capacity of "12.times.5=60 bytes".
As described above, the conventional exposure computing device is arranged to use a multiple-divided integration-type light measuring sensor, to be provided with correction values for making the output of the light measuring sensor into specific values suited for various luminance values, and to carry out an exposure computing operation by using the correction values as applicable. In a case where the number of dividing the light measuring sensor increases and the different integration periods are many in number, an enormous storage capacity becomes necessary for adequately correcting the output of the light measuring sensor. For example, with a memory capacity required for storing a gain correction value per pixel assumed to be 1 byte, if a light measuring sensor divided into 100 pixels is arranged to be capable of coping with three different integration periods, as shown in FIG. 13, the memory must be arranged to have a storage capacity of "100.times.1=100 bytes" for gain correction.
Further, with a memory capacity required for storing a level correction value per pixel assumed to be 1 byte in this case, as shown in FIG. 14, the memory must have a storage capacity of "100.times.3=300 bytes" for level correction. Then, a total storage capacity of the memory required for all correction values becomes 400 bytes.
The conventional arrangement also requires many processes for computing and storing the sensor correction values in the memory within an exposure computing part. A very long period of time thus becomes necessary for adjusting the outputs of the light measuring sensor.